Investigation of Cationic Distribution in Zn1-x Ni x Fe2O4 (x=0.0 to 1.0) by Employing X-ray Absorption Fine Structure Spectroscopy

In the present study, x-ray absorption fine structure (XAFS) spectroscopy has been employed to investigate the cationic distribution in Zn1-x Ni (x) Fe2O4 (x = 0.0 to 1.0) spinel ferrites. The phase purity and lattice parameters of freshly synthesized Zn1-x Ni (x) Fe2O4 were verified by laboratory x-ray diffraction analysis. It is observed that lattice parameters decrease with increase in the Ni concentration, while the system retains cubic symmetry in Fd3m space group. To investigate the local structural environment and cationic distribution, XAFS data were collected at room temperature for the Fe, Zn, and Ni K-edges in Zn1-x Ni (x) Fe2O4, using the x-ray absorption facilities of the Elettra synchrotron source, Trieste, Italy. In the case of Fe, pre-edge features provide valuable information regarding the octahedral or tetrahedral site occupancy, while Zn and Ni edges do not show any appreciable change in the near-edge region. From extended x-ray absorption fine structure (EXAFS) spectroscopy, it is observed that all Zn and Ni atoms occupy tetrahedral and octahedral sites, respectively, whereas Fe atoms occupy octahedral sites in ZnFe2O4 but for the other compositions are present at both octahedral and tetrahedral sites. The occupancy of Fe at octahedral sites decreases with increasing Ni concentration in Zn1-x Ni (x) Fe2O4. These results demonstrate that the local environment of Zn does not show significant variations as the changes at second nearest neighbors are due to Fe and Ni, which have similar scattering factors. However, variations in the Ni surroundings are due to the change of Fe and Zn ratio at A sites, having a relatively larger difference in scattering factor. However, the changes observed in the EXAFS spectra of Fe are a consequence of variation in the occupancy of Fe at tetrahedral and octahedral sites.